Large multi-stranded photographic processing machines are not normally self-threading. A leading edge of the material to be processed has to be pulled and guided through each of the processing stages in the machine. This is normally accomplished by running a continuous belt around the machine to provide a processing path along which the material to be processed is towed. The belt is arranged to run on one side of the processing path. Special spring clips are connected to the belt to which the material is attached. Each clip carries an arm to which the leading edge of the material to be processed is secured for towing through the various processing tanks. After the material has been taken through the processing tanks by the continuous belt, it is detached from the arm and joined on to a take-up spool.